Coal is used as a fuel in many power plants. Before the coal is introduced into the power plant it typically undergoes a pulverization process to reduce the size of the coal from relatively coarse chunks to a fine powder. This is done to increase the reactivity of the coal by increasing the effective surface area, to reduce surface moisture on the coal, and to make transportation of the coal into the furnace forming part of the power plant easier.
The coal is transformed into the above-described fine powder by a pulverizer. There are different types of pulverizers, for example, there are Ball-Type pulverizers, Roll-Bowl or Ball Race Pulverizers, Impact or Hammer Pulverizer Mills, and Attrition Type Pulverizers. Pulverization is the first process in the chain of power generation and is generally time consuming. The pulverizer is employed to dry and crush the correct amount of coal according to the amount of power to be generated. If the pulverizer's operation is compromised, there could be insufficient amounts of pulverized coal or no pulverized coal supplied to the power plant furnace. While Roll-Bowl pulverizers are referred to throughout this disclosure, the disclosure is not limited in this regard as other types of pulverizers known to those skilled in the art to which the disclosure pertains are equally applicable.
Moreover, if the coal output by the pulverizer is not of the required fineness, poor combustion can result causing unburned carbon or large pieces of coal adhering to heat transfer surfaces forming part of a boiler used in a power plant. To date, monitoring the performance of pulverizers has been accomplished via manual inspections. In many cases this has proven inadequate. For example, there is currently no self contained ability for the pulverizer to detect whether or not tramp iron that finds its way into the pulverizer is being properly expelled, or when pieces of tramp iron greater than a predetermined minimum size is encountered. In roll-bowl pulverizers, if tramp iron is not discharged, it repeatedly impacts the grinding rolls as well as the pulverizer body and bowl, potentially damaging these components and impairing the structural integrity of the pulverizer. Normally the presence of tramp iron is detected by an operator listening to the pulverizer. This is highly unreliable.
In most Roll-Bowl type pulverizers, three rolls spaced approximately 120 degrees apart are used to grind the coal. The substantial compressive forces needed to accomplish this grinding are supplied by preloaded springs. If these preloads are not properly set, the rolls will not all exert the same force on the coal, potentially inducing a detrimental vibration situation, as well as reduced pulverizer grinding and fineness capacity. In addition, there is at present, no way to detect whether or not the grinding rolls are worn or damaged. In addition, there currently is no way to detect critical bearing failure, or vibration that indicates that the entire pulverizer is overloaded. Essentially, a raft of operating issues such as, but not limited to those described above can arise in pulverizers and the present means for detecting these issues are outdated and archaic. Currently, there is no method of rapidly determining if there is a fire in a pulverizer. Such fires can damage the pulverizer and cause safety issues for personnel. There is also currently no reliable method for determining if a loss of coal flow has occurred that could change the stoichiometry inside the pulverizer from a fuel rich normal operating regime to a fuel lean operating regime.